The field of the invention pertains to hollow articles such as containers and tubular products of flexible plastic construction and, in particular, to such articles formed with a plurality of sidewall bellows to permit collapse of the container or tubular product. An example of such a container product is disclosed in applicant's U.S. Pat. No. 4,492,313 reissued as U.S. Pat. No. Re 32,379. A number of other examples of collapsible containers are disclosed in the numerous references cited in applicant's reissue patent above.
Bottles manufactured according to applicant's above patent have proven to be successful for a number of plastic materials, however, the folding action causes some plastic materials to crack or craze at the inner fold rings producing grey or cloudy rings in otherwise clear bottles. The cracking or crazing is caused by severe angular deformation of the plastic material at the inner fold rings. While not detracting from the visual appearance of the bottles, the cracking and crazing weakens some bottles although permitting the bottles to fold and latch more easily.
More particularly, as an example, high density polyethylene bottles possess improved latching subsequent to the first or initial collapse after manufacture and the strength of the bottle is not seriously impaired. Polyvinyl chloride bottles, however, are weakened at the inner fold rings after the initial collapse that splits the plastic material. Reusing these bottles therefore would be inadvisable.
Bottles blown from elastomeric materials, polyethylene terepthalate and low density plastics generally do not laminate or craze at the inner fold rings with the initial collapse of the bottle. The bottles retain their strength but, as a result, the latching effect is impaired and the collapse of the bottles is not as effective as with the high density plastics.
With a view toward making the latching effect for collapsible bottles and other hollow articles more effective for a greater variety of plastic materials, applicant has developed the improvements disclosed below.